The present invention relates to corrosion resistant structures and elements, and particularly to a corrosion resistant container suitable for use as an acid resistant electrolytic cell for use in the production, refining and plating of non-ferrous metals.
The present invention is thus particularly, although not exclusively, applicable to the field of electrolytic recovery of metals for which corrosive metal-bearing acid solutions are employed.
Many metals are produced or recovered by the use of electrolysis either from a waste solution or by refining contaminated metal anodes. The production of metals by electrolysis is usually effected in container or "cells" housing a plurality of rows of electrodes (alternately anodes and cathodes). These are immersed, or at least partly immersed in electrolyte and an electric current is passed between adjacent pairs or sets of anodes and cathodes, through the electrolyte, to cause electrolytic deposition of the metal from the electrolyte onto the anode, whilst the cathode is consumed by the ion exchange.
The electrolyte is almost invariably an acid solution of a type which is highly corrosive to the material of the container or cell. In order to resist this corrosion and give the container or cells an extended useful life many attempts have been made in the past to provide the cell walls and floor with a suitable acid resistant coating which is also able to withstand the mechanical abrasion and knocks incurred whilst loading and unloading cells with fresh and spent electrodes respectively, both of which operations have to be performed at regular intervals during use of the cell. Previous attempts to resist the corrosion have, however, been of only limited success so that regular, in some cases frequent, replacement has been necessary. The majority of known protective systems for the cell employ a number of coatings and linings over a base material which is usually a conventional concrete, each layer providing a particular protection. Such cells have required regular maintenance and periodic replacement however, and even in the best cases the coatings have only extended the life of the cell by a relatively short time period of from one to five years, after which the whole structure has to be replaced due to degradation in the base concrete as a result of acid attack. In view of the high cost of metal processing cells such a state of affairs in far from satisfactory.